This invention relates generally to electrolytic reduction cells, and more particularly to apparatus for limiting the extent of vertical movement of the electrode supporting and feeding means of an aluminum reduction cell.
In a conventional arrangement of an aluminum electrolytic reduction cell, one or more carbon anodes, each having a metal shaft embedded therein, is secured by its respective metal shaft to a vertically movable superstructure arranged in superposed relation to the vessel or pot of the electrolytic reduction cell. The cathode structure is usually in the form of collector bars disposed in the bottom of the vessel. During operation of the cell, the carbon anodes are immersed to a predetermined level in the molten electrolyte which forms the electrical path between the anode and cathode of the cell. As electrolytic reduction proceeds, variations in the desired cell voltage are caused by depletion of the alumina ore in the cell as well as consumption of the carbon anodes. To maintain cell voltage relatively constant, the anodes are raised and lowered in the electrolytic bath as necessary by means of hydraulic, pneumatic or electric jacks arranged to vary the vertical position of the anode supporting superstructure. Maintenance of alumina ore concentration within the limits of greatest cell efficiency also requires the periodic addition of controlled amounts of alumina as the ore in the cell is depleted by the reduction process.
Computer monitoring and control of the cell voltage, resistance, ore concentration and other operating parameters of aluminum reduction cells is well-known in the art. Typically, a computer-controlled reduction cell includes automatic means for raising and lowering the anode superstructure. One such system is disclosed in U.S. patent application Ser. No. 298,405, filed Oct. 18, 1972, now U.S. Pat. No. 3,888,747 entitled "Method of and Apparatus for Producing Metal" and assigned to the assignee of the present invention, the description of which is incorporated herein by reference. Should the computer in such a system malfunction or deliver a faulty signal to the jacks, it is possible to cause the anode superstructure to be raised to such an extent that an open cell is created, i.e., one or more anodes is raised out of the molten electrolyte, and, in extreme cases, the superstructure, jacks and associated hardware may be extensively damaged.
Concomitantly with computer control of the vertical position of the anode superstructure in an aluminum reduction cell, there is normally provided parallel means for allowing the cell operator to control the anode jack mechanism. The operator control may be in the form of a manual pushbutton which must be continually depressed to control an electrical, hydraulic or pneumatic system and cause vertical movement of the anode support structure, a voltage meter for monitoring cell voltage and an audible alarm and warning light for indicating the occurrence of an open anode. While the aforementioned cell-operator controls and warning devices are generally sufficient to avoid the open anode condition, there still remains the possiblity of human error in manual control of the jack resulting in extensive damage to the anode support structure and the loss of cell utilization during repairs.